This invention generally relates to a method for partly reinforcing a workpiece and, more particularly, to a method for partly reinforcing a workpiece in which the portion of the workpiece that requires reinforcement is partly reinforced.
With reference to a workpiece with a hole and the hardening technique by jetting cooling water as an example, the background of the invention will be explained below. As a manufacturing technique of a workpiece with a hole, there is known a technique including hole-making step of making a hole through a metallic plate workpiece of an ordinary temperature, and forming step of forming the peripheral area of the hole with the forming surface of a forming die into a formed part of cylindrical shape to be carried out successively.
As concerns a plate-shaped workpiece having a reinforcement requiring part on which stress is liable to be concentrated upon use, recently, there becomes also known a technique of partly hardening the reinforcement requiring part by jetting cooling water in the air toward the high-temperature-heated reinforcement requiring part.
Meanwhile, the above-described peripheral area of the hole is a part on which stress is liable to be localized in use. For this reason, in the case of using a workpiece under such circumstances that stress exerted on the peripheral area of the hole becomes excessive, there is possibility that the peripheral area of the hole may be damaged or deteriorated.
On the other hand, according to the technique of partly hardening the reinforcement requiring part of a workpiece by jetting cooling water in the air toward the reinforcement requiring part after heating up to a high temperature, there are limitations as to realizing partial reinforcement exactly on the spot because a lot of cooling water is also jetted on the other part in addition to the reinforcement requiring part. Further, remaining water in the workpiece may induce corrosion of the workpiece and other defects.